Zhiyuan Zhao

Unique double-shelled hollow silica microspheres: template-guided self-assembly, tunable pore size, high thermal stability, and their application in removal of neutral red

A novel type of monodisperse and double-shelled hollow silica microspheres was reported. This unique double-shelled structure was fabricated using a consecutive template-guided self-assembly. Cationic poly(styrene) (CPS) particles prepared by emulsifier-free polymerization were first used as the template to coat with tetraethylorthosilicate (TEOS) in the presence of coupling agent methacryloxypropyltrimethoxysilane (MPS), forming the core/shell type of CPS/SiO2 particles. The resulting CPS/SiO2 particles were further used as the template and in situ polymerized with styrene, a cationic co-monomer 2-(methacryloyl)ethyltrimethyl ammonium chloride (DMC), followed by electro-statically guided self-assembly and polymerization of TEOS on the surface, generating the sandwich-like CPS/SiO2/CPS/SiO2 particles. Finally, the unique double-shelled hollow silica spheres were produced by one-step removal of the CPS core and CPS layer from the sandwich-like particles. The structure of the monodisperse and intact double-shelled hollow silica microspheres was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET), Elemental Analysis (EA), and 29Si Nuclear Magnetic Resonance (29Si-NMR). Unlike previously reported hollow silica microspheres which have one single shell, the novel silica microspheres have two shells, enabling improved thermal stability and larger BET surface area. Notably, the interior cavity and shell-to-shell distance can be effectively tuned simply by controlling the interior CPS core diameter and the outer CPS template layer. The absorption and separation of the neutral red (NR) in synthesized hollow silica spheres showed favorable adsorption behavior, such as higher absorbent amount of dye and lower rate of dye desorbed for NR in comparison to single-shelled hollow silica, which thereby makes it potentially more applicable in environmental separation and adsorption.

The Fabrication and Development of Molecularly Imprinted Polymer-based Sensors for Environmental Application

The detection of specific molecules as markers of disease, health status, environmental monitoring, and food quality means that MIP-based sensors for these targets attract increasing attention due to their practical significance and their potential application in analytical chemistry. Therefore, considerable endeavors have been devoted to fabricate and develop a variety of MIP sensor platform with high selectivity, sensitivity, and robustness. This review focuses primarily on synthetic strategies and environmental MIP-based sensors, especially emphasizing the development that has occurred in the last decades, in order to help readers to understand and fabricate various optimized MIPs.

One-Pot Pathway: Fabricating Ordered Hollow Silica Spheres Using Sodium Silicate as the Precursor

The preparation of hollow silica spheres via the sodium silicate route presents many advantages such as a low-cost silica source, and an environmentally friendly reaction system. Unfortunately, it is extremely hard to prepare the well-defined hollow silica spheres by using sodium silicate as the silica source owing to its rapid, disordered precipitation under the acid catalysis. As a result, we, in this paper, report a facile, economic, one-pot pathway for preparation of the ordered hollow silica spheres by employing a sodium silicate precursor. In this approach, the cationic polystyrene (CPS) templates can be first prepared via emulsifier-free emulsion polymerization by using the cationic monomer vinylbenzyltrimethylammonium chloride, then, the silica shells were attached on the surfaces of CPS particles via electrostatic interaction, finally CPS particles were in situ dissolved and removed by adding toluene to create ordered hollow silica spheres. Some modern techniques and instruments, including the transmission electron microscope, scanning electron microscopy, infrared spectroscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller theory were employed to monitor and characterize the resulting hollow silica spheres.

Low-cost Hollow Silica Supports for Environmental Pollution: High Removal Capacity and Low Desorption Rate of Neutral Red

Silica-based porous materials are popular adsorbents and have achieved marked success. However, one of the main challenges is surface functionalization for obtaining better removal performances. Therefore, in this paper we developed a hollow silica adsorbent with a well-defined morphology via a sodium silicate route. Compared with the conventional silica-based porous adsorbents prepared by the modified Stober method, the synthesized hollow silica support exhibits many advantages such as low-cost silica source, and using only industrial commodities as starting materials and water as solvent. Excitedly, the resulting matrix can be used as a powerful separation tool to deal with environmental pollution because it is easy to separate from wastewater simply by centrifugation without any modification. The experimental results of absorption and separation on the neutral red indicate that low-cost hollow silica supports can evidently increase dye loading and decrease the rate of dye desorbed in comparison to conventional hollow silica adsorbents obtained via the Stober method.